Recently, as the interest in the global environment and the human living environment has increased and the damage caused by environmental pollution has been recognized, the environmental pollution restoration projects are carried out all over the world and the restoration project market has been growing rapidly.
Restoration of the environment is generally carried out by government regulation and control rather than voluntary, and the introduction of environmental laws and regulations for human health and environmental protection is the driving force for environmental restoration industry.
Recently, as restoration projects for railroad sites have been actively carried out, interest in restoration techniques for not only soil but also ballast has been greatly increased. This is also the result of the concrete regulation of contaminated soil in railroad sites as the Soil Conservation Act is strengthened recently.
The main contaminant sources in the railroad soil are oil spills from the oil storage tanks located on the ground or in the underground, oil spill in the locomotive refueling area, leakages and fugitives of fuels, greases, lubricants, and the like generated from railway vehicles, leachate discharged from waste recycling centers, fugitive oil generated during maintenance of vehicles, and various particulate materials generated during operation. The main contaminant sources in the railroad soil are very diverse and extensive. In order to prevent the contamination of railroad soil, some workplaces have overhauled places of diesel locomotives from which oil leaks out, installed roll pads, FRP or steel plates in railroad vehicle maintenance centers, and paved concrete pavements for railroad vehicle in-out lines. However, this is not an ultimate solution but a temporary measure. Since the railroad workplaces and contamination-inducing facilities are not concentrated but distributed in a wide area and there is a lack of basic data on soil contamination of the railroad sites, it is difficult to grasp the contamination degree and to manage and control the contamination sources. Therefore, it takes a lot of time and money to solve the problem of soil contamination of railroad.
Currently, railroad ballast is used in many sections of domestic and international railway lines, and the railroad ballast is first contaminated because it is laid on the top of the railroad. Particularly, railroad turnouts contaminate the ballast because a considerable amount of lubricant is used. The contaminants on the surface of the ballast move continuously to the bottom of the railroad line due to gravity or rain, and contaminate the roadbed and bottom soil. When the groundwater flowing around the soil is contaminated, the surrounding soil is also contaminated and the contaminated area is gradually enlarged.
Currently, contaminated gravel collected during the replacement work of contaminated railroad ballast is being disposed of in landfills. At this time, most of the collected railroad ballast are designated and buried as designated waste, not general waste, because their surfaces are heavily contaminated. However, since the buried contaminants continue to have adverse effects on the environment over the long term in the form of leachate, landfill gas, odor, etc., it is necessary to separate and treat the contaminants rather than landfill.
As landfill shortage has grown serious gradually, the cost of landfill has been rising steadily. Therefore, there is a growing need for other treatment methods than landfill. In addition, new gravel is needed for the replacement of ballast, and destruction of forests and ecosystems continues to secure new gravel. However, due to the government's strengthened regulations on deforestation and public opinion of environmental groups and the people against the destruction of ecosystems, the supply of new gravel is becoming increasingly difficult. Therefore, there is a growing need for recycling of ballast.
Currently, as technologies to purify contaminated soil and railroad ballast, a thermal treatment method that uses heat to decompose and detoxify contaminants, a microbiological treatment method that activates soil bacteria or promotes the biodegradation of organic compounds by introducing specially developed bacterial strains, soil vaper extraction techniques such as in-situ venting (ISV) or soil vacuum extraction (SVE), which extract polluted air through pores in contaminated soil or gravel, have been developed and utilized. However, these technologies have limitations in expanding their applications because of their low economic feasibility and efficiency.
On the other hand, the proposed patent (Korean Registered Patent No. 10-0614612) discloses a technology that provides an equipment for collecting railroad ballast, an equipment for removing the pollutants on the surface of the railroad ballast by performing blasting on the collected ballast using sand or other media, and an equipment for spraying gravel from which the pollutants are removed on the railroad in the vehicle capable of traveling along the railroad and recycles the railroad ballast by removing the pollutants from the ballast while moving along the railroad. However, although the above method has the merit of being able to purify the railroad ballast on the railroad, it is not easy to use in actual field because it does not have the economic feasibility and efficiency. It does not have high decontamination efficiency because it uses the blasting method.
In order to solve such a problem, the present inventors suggested the technology that separates and purifies contaminants from contaminated soil and ballast by a thermal desorption method using a microwave to secure economic feasibility and to generate heat at a low temperature and a high temperature so that sufficient thermal desorption can be achieved with only one pass regardless of the type of oil through Korean Registered Patent No. 10-1678593. In this patent, the structure of the contaminant desorbing part in which the contaminants are thermally detached is improved so as to include an outer tube and an inner tube. The contaminated ballast passes through the inside of the inner tube and the microwave absorbing and heat generating element is provided on the outer surface of the inner tube so that the contaminants of the surface of the contaminated soil and ballast inside the inner tube are desorbed thermally by irradiating microwave onto the microwave absorbing and heat generating element. A material that is very cheap compared to the price of existing materials and has excellent heat generation efficiency is used as the microwave absorbing and heat generating element, thereby ensuring economic feasibility and purifying the soil contaminated by most oil regardless of the type of oil. However, in this technology, since microwaves are reflected in and leaked out from the space between the outer tube and the inner tube, it may adversely affect the environment. Therefore, it is necessary to improve the above. Also, since the waste heat generated in the contaminants desorption process is released to the outside, there is a need for further improvement in terms of energy efficiency.